Separator for alkaline batteries



2,858,353 Patented Oct. 28, 1958 SEPARATOR FOR ALKALINEvBATTERIES MeyerMendelsohn, New York, N. Y., assignor to Ions Exchange da ChemicalCorp.,New York, N. Y., a corporation of New York No Drawing. Application July6, '1954 Serial No. 441,649

13 Claims. (Cl. 136-146) My present invention relates to inter-electrodeseparators for alkaline batteries,.e., g. batteries of the silverzinctype in which the electrodes are closely confined in a casing and areapplied under pressureagainst semi-permeable membranes.

Sheets of methyl cellulose are excellent separators for alkalinebatteries of the aforementioned type, because of the fact that theyresist oxidation,by:-silver peroxide. as Well as penetration by Zinc.high resistance of methyl cellulose film, however, little use has beenmade in the past of separators of this kind.

My invention has for its object the provision of a methyl cellulose filmwhosereisistanceis lowenough to enable the use of such film as aseparator in a high-elliciency battery particularly (but notexclusively) of the aforementioned silver-zinc type.

I have found, in accordance with this invention, that the desiredlow-resistance methyl cellulose film can be obtained by admixing anaqueous solution of a water-soluble alkali salt of a polymeric compoundwith an aqueous methyl cellulose solution. For purposes of thisdisclosure, and in keeping with established practice, the term alkali isintended to embrace not only the alkali metals proper, such as sodium orpotassium, but also ammonium.

The water-soluble alkali salt of this invention may be, morespecifically, a salt of alginic acid or of a sulfonated polystyrene orderivative thereof. The last-mentioned group includes, moreparticularly, an alkali salt of a sulfonated polystyrene, e. g. of acompound which is commercially available under the name Lustrex.Reference is also made to my co-pending application Ser. No. 349,091,filed April 15, 1953, which discloses a process of sulfonatingpolystyrene and other high polymers in the presence of silver oxide;neutralization of the resulting sulfonic and sulfuric acids, e. g. bymeans of sodium or ammonium hydroxide, yields aqueous solutions ofsodium or ammoniumsalts, respectively, of sulfonated polystyrene similarto the aforementioned Lustrex .compounds.

It may be mentioned that the use of ammonium salts is not recommended inthe presence of electrodes containing silver.

If a very flexible film is desired, a plasticizer can be incorporated inthe modified methyl cellulose film.

EXAMPLE I EXAMPLE II Equal parts of an 8% aqueous solution of methylcellulose and of a 20% aqueous solution of Lustrex, or of a sodium,potassium or ammonium salt obtained in the manner described above withreference to my co-pending ap- Because of the relatively ite). Abilitytoresist strongly alkaline electrolytes;

plicationSer. No, 349,091, are mixed together and cast into a film,optionally with the addition of a plasticizer as set forth in thepreceding example.

The resistance-reducing additives according to'this invention, and inparticular the alkali salts specifically disclosed herein, have incommon the following desirable properties:

(a) Abundance of ionogenic groups; (b) High oxidation resistance;

that a film containing 0% additive (100% methyl cellulose) has a tensilestrength ofthe order of 900 kg./cm. coupled with a very high resistancein excess of 45 -'ohmscm. With progressively larger additive ratiosthe'resistance' falls to a fraction-of its original valueythe limit ofthe useful range being reached when the film becomes too fragile forhandling;

'Table I vMethyl Electrical Tensile Alginate, parts i Cellulose.'Eeslst- Strength,

parts ance, kg./cm.

ohms-cm.

100 over 45 895 89 7. 2 415 3. 9 375 67 1. 9 325 33 0.08 250 25negligible Useful range of ratio (parts by weight)alginate/methyl-cellulose: Approximately 1:10 to 2:1.

Table [1 Methyl Electrical Tensile Lustrex, parts Cellulose, Resist-Strength, parts ance, kg./cm.

ohms-cm.

100 over 45 895 0 negligible Useful range of ratio (parts by weight)Lustrex/methyl-cellulose: Approximately 1:10 to 10:1.

Separators according to the invention may, of course, be used inalkaline electrolytic systems other than batteries. The concentrationsset forth in the examples are subject to considerable variations and aremerely illustrative of conditions under which a good film can normallybe obtained.

I claim:

1. A semi-permeable sheet incorporating a mixture of methyl celluloseand an alkali salt of a polymeric compound selected from the group whichconsists of alginic acid and sulfonated polystyrene.

2. A semi-permeable sheet incorporating a mixture of methyl cellulose,an alkali salt of a polymeric compound selected from the group whichconsists of alginic acid and sulfonated polystyrene, and a plasticizer.

3. A semi-permeable sheet incorporating a mixture of methyl cellulose,an alkali salt of a polymeric compound selected from the group whichconsists of alginic acid and sulfonated polystyrene, and a glycolplasticizer.

4. A semi-permeable sheet incorporating a mixture of methyl celluloseand an alkali alginate.

5. A semi-permeable sheet incorporating a mixture of methyl cellulose,an alkali alginate and a glycol plasticlzer.

6. A semi-permeable sheet incorporating a mixture of methyl celluloseand an alkali alginate, said alginate being present in a proportionranging between substantially and 200%, by weight, of said methylcellulose.

7. A semi-permeable sheet incorporating a mixture of methyl cellulose,an alkali alginate and a glycol plasticizer, said alginate being presentin a proportion ranging between substantially 10% and 200%, by weight,of said methyl cellulose.

8. A semi-permeable sheet incorporating a mixture of methyl celluloseand an alkali salt of sulfonated polystyrene.

9. A semi-permeable sheet incorporating a mixture of methyl cellulose,an alkali salt of sulfonated polystyrene and a glycol plasticizer.

10. A semi-permeable sheet incorporating a mixture of methyl celluloseand an alkali salt of sulfonated polystyrene, said alkali salt beingpresent in a proportion ranging between substantially 10% and 1000%, byweight, of said methyl cellulose.

11. A semi-permeable sheet incorporating a mixture of methyl cellulose,an alkali salt of sulfonated polystyrene and a glycol plasticizer, saidalkali salt being present in a proportion ranging between substantially10% and 1000% by weight, of said methyl cellulose.

12. A process for making a separator for alkaline batteries, comprisingthe steps of admixing an aqueous solution of a. water-soluble alkalisalt of a polymeric compound with an aqueous solution of methylcellulose, said polymer being selected from the group which consists ofalginic acid and sulfonated polystyrene, and casting the mixture into afilm.

13. A process for making a separator for alkaline batteries, comprisingthe steps of admixing an aqueous solution of a water-soluble alkali saltof a polymeric compound and a glycol plasticizer with an aqueoussolution of methyl cellulose, said polymeric compound being selectedfrom the group which consists of alginic acid and sulfonatedpolystyrene, and casting the mixture into a film.

References Cited in the file of this patent UNITED STATES PATENTS2,161,561 Dalton June 6, 1939 2,482,062 Hanson Sept. 13, 1949 2,487,106Cornwell Nov. 8, 1949 2,534,336 Cabon Dec. 19, 1950 2,607,809 Pitzer aAug. 19, 1952 2,636,851 Juda et al Apr. 28, 1953 2,653,985 PhilippsSept. 29, 1953 2,653,987 Baty Sept. 29, 1953 2,662,929 Dague Dec. 15,1953 2,673,887 Booth Mar. 30, 1954 2,678,961 Uhlig et al. May 18, 19542,696,515 Koren et al. Dec. 7, 1954 2,747,009 Kirkwood et al. May 22,1956 FOREIGN PATENTS 708,350 Great Britain May 5, 1954

1. A SEMI-PERMEABLE SHEET INCORPORATIONG A MIXTURE OF METHYL CELLULOSEAND AN ALKALI SALT OF A POLYMERIC COMPOUND SELECTED FROM THE GROUP WHICHCONSISTS OF ALGINIC ACID AND SULFONATED POLYSTYRENE.